I had some hackberry do the very same thing. The whole tree was affected in the outer inch or so of sapwood, so all my staves from it are being chased down to "the good stuff" before i continue. My tree was cut in May, split shortly thereafter and kept outta the elements. In fact, the stave that first blew on me had primo treatment. I can only figure it had been attacked and the damage done before i ever cut it. Looking back, the outer sapwood looked porous even from the first cut and debarking, but i figured it was the way it was supposed to look since it was my first harvest (of anything, let alone a whitewood).
Does the integrity of the rings get better as you go down to the center?